The invention concerns a method for manufacturing a concave skip body, or more specifically, a skip body with a concave cross section and a continuous inwardly curved base from one large sheet of metal, thereby allowing unitary construction.
Concave skip bodies are presently shaped by bending. The concave shape of the transverse section results from performing a succession of longitudinal bending operations which impart a polygonal shape to the body.
This succession of creases is unsatisfactory for several reasons.
First, the interior structure of a shaped skip body which is in contact with the cargo should be as smooth as possible, with no bulging areas to attract residue which could adhere to the metal when freight is discharged and adversely affect wear over time. It is preferable for no residue to remain on the structure, since it could interact with the next shipment to be transported.
Furthermore, the utmost care is required when bending certain metals such as aluminum.
Moreover, other metals of interest, such as highly flexible steel known as HLE or THLE, will not maintain a definitive form unless they are bent into shape. The use of such metals is particularly exacting when shaping long objects that are hard to form of one piece, such as skip bodies. Large sheets of these metals have proven extremely difficult, if not impossible, to shape in any way other than by bending them on forms designed to interlock in the same way a skip body fits onto its complementary cradle receptor.
In addition, because of these complementary shapes, the creases in the skip body and in the cradle must be perfectly concentric. This technique requires the use of precise machinery that is very cumbersome.
Thus, the only choices remaining are to either use smaller dimensions or continue using the bending technique despite its many disadvantages.
However, the metals discussed above also have many qualities that make them preferable to conventional metals.
Practically speaking, because of its lower density, a vehicle using aluminum can carry a heavier load. For this reason many transport vehicles already use trailers, semi-trailers and skip bodies made primarily of aluminum.
These skip bodies are all conventionally designed and are generally rectangular in shape, with multiple reinforcing structures.
For other reasons, highly flexible steel is one of the preferred metals for constructing skip bodies.
While there is a serious risk that aluminum will fissure when creased, highly flexible steel is also very unsuitably for bending and is actually so resistant that it is impossible to bend using present methods.
However, both highly flexible steel known by the acronym HLE and very highly flexible steel known as THLE offer two advantages that make them very desirable for skip body construction: they are highly mechanically resistant to shocks and punctures, a quality which is particularly useful for skip bodies transporting heavy loads, minimizing the risk of damage when heavy freight is discharged and performing well in nearly any application; the steel is highly resistant to abrasion.
The high resistance of this metal provides greater weight while at the same time decreasing cost, since thinner metal can be used.
However, these same advantages precipitate manufacturing problems.
The flexible steel has a spring-like quality which not only resists precise formation into such a definitive, unnatural, shape, but also resists maintaining the curved shape.
The specific problem addressed here is how to achieve an industrial process for manufacturing skip bodies with a consistent inwardly curved, continuously convex shape, essentially semi-elliptical, with a certain degree of precision and using a reproducible operation.
The present invention relates to an industrial process for manufacturing a skip body from a single sheet of metal or several adjacent sheets seamed either longitudinally or transversely, manipulated and shaped as a single element.
More specifically, the invention relates to a method for forming a skip body from a large sheet of metal with a continuously curved, concave cross-section without creasing it, characterized by the following steps: a large sheet (1) of metal is prepared from one piece or several joined pieces; the single sheet (1) of metal is curved inwardly using maintenance means (4, 5) into a cross section approximating the definitive shape desired for the ultimate shape of the body (3) of the skip; a sealing plate (10) is secured to one of the extremities (9) of the skip body, the contours (11) of which have the exact concave shape to be obtained, by gradually applying the edges of the opening of this end of the metal sheet against the cut edges of sealing plate (10) during the installation process; the opposed extremity (12) of the skip body is stiffened by means of a stiffening member (13) according to the definitive shape to be reached; the stiffening of its longitudinal edges is longitudinal edges is performed either before or after the metal is curved inwardly; the pressure of the maintenance means is relaxed and the skip body (3) is disengaged, having assumed its definitive shape.
The present invention makes is possible to fabricate a concave skip body that is continuously curved, with no creases, from a large sheet of any type of metal suitable for manufacturing skips, and more specifically from any of the preferred metals such as aluminum and highly flexible steel.